So, you have "feral" chickens?

Yes.
How does a domesticated bird become "feral"?
Good question.  Let's revisit the definition of "feral". The word feral has two meanings. In this case we are using it as an adjective as in "a pack of feral dogs roamed the woods".  Feral means that a domesticated animal has reverted back to it's wild/natural state.  So then, it shouldn't surprise us that any animal that has been domesticated can become "feral".
You are talking about your chickens, right???
Yes.
I just have to ask, how did it happen?
That's fine, I was hoping someone would ask.  So, we had this skunk that ate two birds.  The birds started roosting in the rafters after that.  Then we had an opposum that ate at least three birds.  Then the birds decided that it was safer outside the coop than inside...and they roosted on the deck rail next to the patio door on the farmhouse.  It was at that point that the chickens simply wouldnt go to the barn. Nothing could entice them...food, drink, implements on which to poop.  Absolutely no reason was good enough for them to go back there.  The Wife watched as they began foraging in the woods for food.  Roosting in trees during the day if they needed safety.  They no longer eat the layer feed.  We have no idea if they are laying eggs...those darned birds live in the woods in the day (feral) and roost on the deck rail at night.
Wow.  So, you have "feral" chickens.  Never heard of it before.
Neither had we.